1. Field of the Invention
The present invention relates to a zoom lens used in a liquid crystal projector, a silver halide camera, a digital single reflex camera, and the like.
2. Description of the Related Art
It is known that an optical system that has telephoto zooming ability and whose basic aberrations are adjusted can be obtained by arranging a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and subsequent lens units. In general, in optical systems, it is difficult to achieve a small size and a high performance. In particular, with an optical system having the aforementioned refractive power structure, it is difficult to achieve a small size while correcting axial chromatic aberration and transverse chromatic aberration at the telephoto end. Regarding such a problem, Japanese Patent Application Laid-Open No.: 2006-349947 and Japanese Patent Application Laid-Open No.: 2007-298555 describe optical systems whose axial chromatic aberration and transverse chromatic aberration may be corrected by using an anomalous dispersion material. With the optical systems described in Japanese Patent Applications Laid-Open Nos. 2006-349947 and 2007-298555, axial chromatic aberration and transverse chromatic aberration are corrected by using an anomalous dispersion material having a positive refractive power and a high partial dispersion ratio in a first lens unit.
With the optical systems described in Japanese Patent Applications Laid-Open Nos. 2006-349947 and 2007-298555, the correction of axial chromatic aberration and transverse chromatic aberration may be acceptable for certain applications. However, a higher image quality is required for digital single-lens reflex (DSLR) cameras and the like, and therefore further improvement in optical performance is required for such apparatuses.